gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-1987, 1989, 1991, 1994-1996, 1998, 2000-2005,
   4    2007-2012 Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21 /* This file defines functions (and commands to exercise those
  22    functions) for reading debugging information from object files
  23    whose images are mapped directly into the inferior's memory.  For
  24    example, the Linux kernel maps a "syscall DSO" into each process's
  25    address space; this DSO provides kernel-specific code for some
  26    system calls.
  27
  28    At the moment, BFD only has functions for parsing object files from
  29    memory for the ELF format, even though the general idea isn't
  30    ELF-specific.  This means that BFD only provides the functions GDB
  31    needs when configured for ELF-based targets.  So these functions
  32    may only be compiled on ELF-based targets.
  33
  34    GDB has no idea whether it has been configured for an ELF-based
  35    target or not: it just tries to handle whatever files it is given.
  36    But this means there are no preprocessor symbols on which we could
  37    make these functions' compilation conditional.
  38
  39    So, for the time being, we put these functions alone in this file,
  40    and have .mt files reference them as appropriate.  In the future, I
  41    hope BFD will provide a format-independent bfd_from_remote_memory
  42    entry point.  */
  43
  44
  45 #include "defs.h"
  46 #include "symtab.h"
  47 #include "gdbcore.h"
  48 #include "objfiles.h"
  49 #include "exceptions.h"
  50 #include "gdbcmd.h"
  51 #include "target.h"
  52 #include "value.h"
  53 #include "symfile.h"
  54 #include "observer.h"
  55 #include "auxv.h"
  56 #include "elf/common.h"
  57 #include "gdb_bfd.h"
  58
  59 /* Verify parameters of target_read_memory_bfd and target_read_memory are
  60    compatible.  */
  61
  62 gdb_static_assert (sizeof (CORE_ADDR) == sizeof (bfd_vma));
  63 gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte));
  64 gdb_static_assert (sizeof (ssize_t) <= sizeof (bfd_size_type));
  65
  66 /* Provide bfd/ compatible prototype for target_read_memory.  Casting would not
  67    be enough as LEN width may differ.  */
  68
  69 static int
  70 target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
  71 {
  72   /* MYADDR must be already allocated for the LEN size so it has to fit in
  73      ssize_t.  */
  74   gdb_assert ((ssize_t) len == len);
  75
  76   return target_read_memory (memaddr, myaddr, len);
  77 }
  78
  79 /* Read inferior memory at ADDR to find the header of a loaded object file
  80    and read its in-core symbols out of inferior memory.  TEMPL is a bfd
  81    representing the target's format.  NAME is the name to use for this
  82    symbol file in messages; it can be NULL or a malloc-allocated string
  83    which will be attached to the BFD.  */
  84 static struct objfile *
  85 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
  86                              int from_tty)
  87 {
  88   struct objfile *objf;
  89   struct bfd *nbfd;
  90   struct bfd_section *sec;
  91   bfd_vma loadbase;
  92   struct section_addr_info *sai;
  93   unsigned int i;
  94   struct cleanup *cleanup;
  95
  96   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  97     error (_("add-symbol-file-from-memory not supported for this target"));
  98
  99   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
 100                                          target_read_memory_bfd);
 101   if (nbfd == NULL)
 102     error (_("Failed to read a valid object file image from memory."));
 103
 104   gdb_bfd_ref (nbfd);
 105   if (name == NULL)
 106     nbfd->filename = "shared object read from target memory";
 107   else
 108     {
 109       nbfd->filename = name;
 110       gdb_bfd_stash_filename (nbfd);
 111       xfree (name);
 112     }
 113
 114   if (!bfd_check_format (nbfd, bfd_object))
 115     {
 116       make_cleanup_bfd_unref (nbfd);
 117       error (_("Got object file from memory but can't read symbols: %s."),
 118              bfd_errmsg (bfd_get_error ()));
 119     }
 120
 121   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 122   cleanup = make_cleanup (xfree, sai);
 123   i = 0;
 124   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 125     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 126       {
 127         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 128         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 129         sai->other[i].sectindex = sec->index;
 130         ++i;
 131       }
 132
 133   objf = symbol_file_add_from_bfd (nbfd, from_tty ? SYMFILE_VERBOSE : 0,
 134                                    sai, OBJF_SHARED, NULL);
 135
 136   /* This might change our ideas about frames already looked at.  */
 137   reinit_frame_cache ();
 138
 139   do_cleanups (cleanup);
 140   return objf;
 141 }
 142
 143
 144 static void
 145 add_symbol_file_from_memory_command (char *args, int from_tty)
 146 {
 147   CORE_ADDR addr;
 148   struct bfd *templ;
 149
 150   if (args == NULL)
 151     error (_("add-symbol-file-from-memory requires an expression argument"));
 152
 153   addr = parse_and_eval_address (args);
 154
 155   /* We need some representative bfd to know the target we are looking at.  */
 156   if (symfile_objfile != NULL)
 157     templ = symfile_objfile->obfd;
 158   else
 159     templ = exec_bfd;
 160   if (templ == NULL)
 161     error (_("Must use symbol-file or exec-file "
 162              "before add-symbol-file-from-memory."));
 163
 164   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 165 }
 166
 167 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 168
 169 struct symbol_file_add_from_memory_args
 170 {
 171   struct bfd *bfd;
 172   CORE_ADDR sysinfo_ehdr;
 173   char *name;
 174   int from_tty;
 175 };
 176
 177 /* Wrapper function for symbol_file_add_from_memory, for
 178    catch_exceptions.  */
 179
 180 static int
 181 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 182 {
 183   struct symbol_file_add_from_memory_args *args = data;
 184
 185   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 186                                args->from_tty);
 187   return 0;
 188 }
 189
 190 /* Try to add the symbols for the vsyscall page, if there is one.
 191    This function is called via the inferior_created observer.  */
 192
 193 static void
 194 add_vsyscall_page (struct target_ops *target, int from_tty)
 195 {
 196   CORE_ADDR sysinfo_ehdr;
 197
 198   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 199       && sysinfo_ehdr != (CORE_ADDR) 0)
 200     {
 201       struct bfd *bfd;
 202       struct symbol_file_add_from_memory_args args;
 203
 204       if (core_bfd != NULL)
 205         bfd = core_bfd;
 206       else if (exec_bfd != NULL)
 207         bfd = exec_bfd;
 208       else
 209        /* FIXME: cagney/2004-05-06: Should not require an existing
 210           BFD when trying to create a run-time BFD of the VSYSCALL
 211           page in the inferior.  Unfortunately that's the current
 212           interface so for the moment bail.  Introducing a
 213           ``bfd_runtime'' (a BFD created using the loaded image) file
 214           format should fix this.  */
 215         {
 216           warning (_("Could not load vsyscall page "
 217                      "because no executable was specified\n"
 218                      "try using the \"file\" command first."));
 219           return;
 220         }
 221       args.bfd = bfd;
 222       args.sysinfo_ehdr = sysinfo_ehdr;
 223       args.name = xstrprintf ("system-supplied DSO at %s",
 224                               paddress (target_gdbarch, sysinfo_ehdr));
 225       /* Pass zero for FROM_TTY, because the action of loading the
 226          vsyscall DSO was not triggered by the user, even if the user
 227          typed "run" at the TTY.  */
 228       args.from_tty = 0;
 229       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 230                         &args, RETURN_MASK_ALL);
 231     }
 232 }
 233
 234 \f
 235
 236 /* Provide a prototype to silence -Wmissing-prototypes.  */
 237 extern initialize_file_ftype _initialize_symfile_mem;
 238
 239 void
 240 _initialize_symfile_mem (void)
 241 {
 242   add_cmd ("add-symbol-file-from-memory", class_files,
 243            add_symbol_file_from_memory_command,
 244            _("Load the symbols out of memory from a "
 245              "dynamically loaded object file.\n"
 246              "Give an expression for the address "
 247              "of the file's shared object file header."),
 248            &cmdlist);
 249
 250   /* Want to know of each new inferior so that its vsyscall info can
 251      be extracted.  */
 252   observer_attach_inferior_created (add_vsyscall_page);
 253 }